Solar accumulators with a plane solar heat collector are used for utilizing direct solar radiation as well as diffuse sky radiation. Plane solar heat collectors comprise a radiation absorbent plate with ducts for heat carriers, which act as transmitted to the heating agent. The heat energy which is collected in this way in then used directly by a heat consumption unit, for example a hot water preparator for tap hot water, but it can also be conveyed to the vaporization system of a heat pump or the like. During the warm season of the ywar a substantial part of the collected heat can also be conveyed to one or several accumulators. Low temperature systems of the afore mentioned kind however demand accumulators with large volumes, which causes high investment costs and an increased space requirement. Besides an extensive pipe line system is required as the accumulator tank usually is placed within spaces such as a basement, outhouse or the like, which are located at a considerable distance from the solar collectors.